This invention relates in general to video systems and, in particular, to video systems including a television (TV) receiver, a teletext (TTX) processor and an external source of red, blue and green (RGB) color signals.
Modern television receivers are increasingly being constructed with microprocessor controlled functions. A modern video system may include a TV receiver, a video cassette recorder (VCR) and a TTX processor; may be able to process signals from a number of RF and baseband input sources; and may also be capable of processing RGB signals from an external source such as a personal computer. Source selection, tuning and control of all functions of the TV receiver, VCR and TTX processor may all be controlled from a keyboard located on a central control unit. The system may also be controlled from a remote location over a wireless link.
Many of the controls and circuit functions of the TV receiver may be "digitized" to enable appropriate data to be rapidly processed and transferred back and forth along two-way communication links or buses under control of one or more microprocessors. As such systems become more complex, the data transfer and switching requirements and the burden on the microprocessors increase, especially that on the central or control microprocessor. If the burden becomes excessive, it can complicate the software and increase the system processing time. Further, many of the functional elements in the video system are individually fabricated as standard integrated circuit chips and it is often difficult (and costly) to add to or change existing features or functions on the chip.
In the video system described in the copending application referred to above, the control microprocessor is relieved of a portion of the task of generating on-screen displays by adding a read only memory (ROM) to the TTX processor for those displays. When required, the control microprocessor addresses the TTX ROM for loading the selected, encoded display data into the TTX display memory and the on-screen display is then generated by the TTX processor. Thus, the unused capacity of the TTX processor is enlisted to relieve the control microprocessor of the burden of producing such on-screen displays.
In the present invention, the TTX processor of the video system is also used for switching the inputs of an external RGB source.